This invention relates to an image forming apparatus using a web-like (longitudinal or roll type) photosensitive recording medium, and more particularly to an image forming apparatus having a control unit for selectively performing a rewinding operation after a developing process of the medium.
There has been well known a conventional image forming apparatus such as a copying machine in which a photosensitive and pressure-sensitive recording sheet coated with microcapsules encapsulating dye precursor therein is exposed to light to form a latent image thereon, and then superposed over a developer sheet coated with developer material color-reactable with the dye precursor under pressure to pressure-develop the latent image on the photosensitive and pressure-sensitive recording medium into a visible image on the developer sheet.
FIG. 1 shows this type of image forming apparatus. As shown in FIG. 1, the apparatus includes a body frame 1 having an upper portion provided with an original support glass plate 2 for mounting thereon an original, and a cover 3 for opening and closing the original support glass plate 2. The glass plate 2 and the cover 3 are movable in a horizontal direction. A light source 5 including a halogen lamp 4 and reflectors 5 is provided below the original support glass plate 2. The halogen lamp 4 is adapted for irradiating white light to the original on the glass plate 2 and extends in a direction perpendicular to the moving direction of the original support glass plate 2. The reflectors 6 are adapted to direct light emitted from the halogen lamp 5 through the original support glass plate 2 to the original to thereby effectively use the white light. At a right side of the halogen lamp 4 are provided a cooling unit 20 comprising a fan and a louver for cooling the halogen lamp 4. During light irradiation from the halogen lamp 4, the original support glass plate 2 is moved in horizontal direction, so that an entire area of the original is scanned with the light.
An exposure stand 7 is disposed at an internal central portion of the body frame 1. Further, a color filter unit 8 for adjusting a color tone and a focusing lens unit 9 are disposed between the light source 6 and the exposure stand 7. These color filter 8 and the lens unit 9 are supported by an attachment plate 10. A pair of reflection mirrors 11a and 11b are disposed between the lens unit 9 and the exposure stand 7 for adjusting a light path length and focal length. These reflection mirrors 11a and 11b are movably supported on an attachment member 12. The light from the light source 6 is reflected from the original and is directed toward the exposure stand 7 through the color filter 8, the lens unit 9 and the reflection mirrors 11a and 11b. The above exposing elements constituting an exposure system and are shielded from other elements by a light-shielding plate 35.
A sheet cartridge 28 is detachably provided at an upper internal space of the body frame 1. An elongated web-like photosensitive sheet 13 is accommodated in the sheet cartridge 28 such that it is wound around a shaft 14 in a rolled state. As the photosensitive sheet is used a microcapsule sheet coated with a plurality of microcapsules which encapsulate therein chromogenic material or dye precursor. Beside the sheet cartridge 28, there is provided a takeup shaft 15 which is rotatable for winding the microcapsule sheet 13 thereover. Plural sheet feed rollers 16 are rotatably provided to feed and guide the microcapsule sheet 13 through a sheet feed guide 33 and the exposure stand 7 to the takeup shaft 15. The microcapsule sheet 13 drawn out of the sheet cartridge 28 is wound over the takeup shaft 15. During the travel of the sheet 13, it passes along a lower surface of the exposure stand 7 at which the sheet 13 is exposed to an image light reflected from the original for forming a latent image corresponding to an image of the original.
A sheet cassette 18 is detachably provided at a lower inner portion of the body frame 1 and below the exposure stand 7. The sheet cassette 18 is adapted for storing a stack of cut developer sheets 17 each being coated with developer material thereon and having a predetermined size.
A pressure developing unit 19 is disposed at a position between the exposure stand 7 and the takeup shaft 15. In the pressure developing unit 19, the light-exposed microcapsule sheet 13 is superposed with each developer sheet 17 under pressure, so that the non-light exposed microcapsules on the microcapsule sheet 13 are ruptured to induce a chromogenic reaction between the dye precursor issued from the ruptured microcapsules and the developer material coated on the developer sheet 17. As a result, a color output image is formed on the developer sheet 17.
A sector roller 21a (or a suction type of sheet pickup unit) is further provided above the cassette 18 for picking up and feeding the developer sheets 18 one by one. Further, a plurality of feed rollers 21 and a sheet guide 25 are provided between the sheet cassette 18 and the pressure developing unit 19 for transferring the developer sheet 17 from the cassette 18 to the developing unit 19.
At an exit side of the pressure developing unit 19, a separation roller 22 is provided for separating the developer sheet 17 from the microcapsule sheet 13. Further, a heat-fixing unit 23 is disposed downstream of the pressure developing unit 19 for heat-fixing an output image provided on the developer sheet 17. Furthermore, a discharge tray 24 is provided at an extreme end portion of a developer sheet path for receiving the developer sheet 17 which has been subjected to a heat-fixing treatment in the heat-fixing unit 23.
In the image forming apparatus thus constructed, an image forming developing process is substantially completed after a trailing end of a light-exposed area (image area) of the microcapsule sheet 13 is subjected to a pressure developing process in the pressure-developing unit 19 and fed over the separation roller 22 while the microcapsule sheet 13 is superposed with the developer sheet 17. Therefore, the microcapsule sheet 13 can not be subjected to a subsequent exposure process until it is fed over the separation roller 22. In other words, an area between the trailing end 7a of an image area formed in an exposure process and the leading end of another image area formed of the subsequent exposure process is not exposed to the light, that is, is not used to an image forming process. This is vain use of the microcapsule sheet.
In order to effectively use the microcapsule sheet 13, after the trailing end of an image area of a previous exposure process is fed over the separation roller 22, the microcapsule sheet 13 is rewound by rotating the shaft 14 in a reverse direction (counterclockwisely in FIG. 1) until the trailing end portion of the image area of the previous exposure process is fed to the exposure stand 7 (for example, the trailing end portion is rewound between a rewinding path as indicated by arrows A and B as shown in FIG. 1). This rewinding operation enables an effective use of the microcapsule sheet and a remarkable reduction in running cost.
As described above, the rewinding operation of the microcapsule sheet requires the microcapsule sheet to be rewound after an image forming process, however, a rewinding speed of the rewinding operation can not be increased because the microcapsule sheet is supplied with a large tension to prevent the slack thereof and high accurate adjustment is required for the rewinding operation. Accordingly, it takes a long time to perform an image forming process in the conventional image forming apparatus.